The study of bariatric surgery offers unique opportunities to evaluate the effects of weight loss among very obese individuals and how this influences quality of life, including impact on co-morbidities of obesity. This proposal is submitted as a collaborative effort of the Department of Medicine, Obesity and Nutrition Research Center (ONRC) and the Department of Epidemiology Prevention Center and Preventive Cardiology Program. We believe that the future studies of bariatric surgery have three important components. First, what is the long term outcome of bariatric surgery in terms of quality of life, morbidity and mortality and are there differences in outcome by type of surgery and characteristics of individuals having the surgery, especially in relationship to distribution of body weight and insulin resistance (IR). The most important health risks for obese individuals are related to cardiovascular disease (CVD). Obesity has been reported to be an independent risk factor for congestive heart failure (CHF) and also for hypertension, type 2 diabetes mellitus, and their complications. Second, the study of bariatric patients offers a unique opportunity to study the metabolic changes associated with obesity and weight loss especially in relationship to carbohydrate and fat metabolism. Third, it is important to try and determine the reasons why many patients can successfully maintain substantial weight loss with minimal co-morbidity after bariatric surgery and especially the potential importance of gastrointestinal physiology and CNS effects on maintaining long-term weight loss. The University of Pittsburgh Bariatric Surgery Program is one of the largest and most successful in the United States. We have excellent follow up of participants and have developed a major collaborative program within the University of Pittsburgh and other institutions. The ONRC is a major National Institutes of Health (NIH)-funded research program dedicated to the study of the pathophysiology of obesity and diabetes and to behavioral research both related to enhancing weight loss and exercise and studying the long term behavioral aspects of these interventions. The Cardiovascular Epidemiology Program in the Department of Epidemiology has extensive experience in observational and clinical trials with a special interest in the measurement of vascular disease.